As of the computers being used, there is a requirement to identify the functions, which are desired to be done, to the computer. In the beginning, the functions expected from the computers were informed to the computers via punched cards. The said punched cards are one of the primitive examples of data storage systems. The limited capacity of the punched cards made necessary to develop different data storage ways. The magnetic tapes having more data capacity than the punched cards have been developed for this need. Data, which can be stored in ten thousand punched cards, can be stored in some magnetic tapes. After magnetic tapes, the diskettes having a magnetic disc therein have been developed. The said diskettes provide carrying the data as well as storing them. However, the said diskettes are not convenient to store data locally because of their limited capacity. Devices which are called hard drives and include storage area and reading/writing head therein have been developed for local storage in computers. With the increasing capacity need, the number of the storage areas within the hard drives and the data amount that can be stored in unit area of the storage unit have been increased. The said increases enable the capacity to be increased. The number of the read/write heads has also been increased in order to increase the access speed to the data stored in the said hard drives. With the increase in need to carry the data, the capacity of the portable media has also increased. CD; DVD. Blue-Ray etc. can be given as example for the said media.
Even though the capacities of the data storage media have increased, there is still need for storage area so large that it cannot be met by the said media. Especially the datacenters need storage area in very high capacities. Furthermore, access speed and recording speed of the said data is also important as well as the content on the stored data in order that the services to be served using the stored data will be fast.
Magnetic data storage operates based on changing the orientations of the magnetic dipoles. The magnetic domains wherein the orientations of all magnetic dipoles are same represent one bit. In optical storing methods, craters and non-crater areas present on the surface of the optical medium represent bits.
In the state of the art, there are optomagnetic (or magneto-optic) data storage units the orientation of the magnetic dipoles of which can be changed optically. Recording in the said storage area is realized on a ferromagnetic material coated on a disc. This ferromagnetic material is generally located inside the sheath which preserves it from dust. The biggest problems of magnetic storage units are the storage areas. One of the reasons for this size problem is that in case the recording density on a recording medium (data amount on a unit area) exceeds a determined value, the interaction between the bits increases and the thermal stability decreases. The said problem is generally called as superparamagnetic effect. One way to overcome this superparamagnetic effect is to use recording media having a high magnetic anisotropic energy density. However, this requires using high magnetic fields to change the magnetization of the recording medium that will not be practical.
Japanese Patent document no JP62184644, an application known in the state of the art, discloses a medium for optomagnetic memory. The said medium can easily be rewritten and it is stable against the outer magnetic fields. In the said document, it is disclosed that a laser light is focused to a film by a lens, and the film is heated by means of the focused laser light. Therefore, antiferromagnetic layer demagnetizes. In the meantime, by means of an external magnetic field applied on the film, the said desired information can be written on this area, the information which is written can remain here when the related area is cooled.
United States Patent document no US20110058458, an application known in the state of the art, discloses magneto-optical switching device for switching magnetization in a medium, comprising a magnetizable medium.
In the article titled “All-Optical Magnetic Recording with Circularly Polarized Light” (C. D. Stanciu et. Al., PRL 99, 047601 (2007)), in the state of the art, a study is disclosed wherein the magnetization can be reversed using 40 femtoseconds laser pulses, without applying any magnetic field.
In the article titled “Spin-polarized light-emitting diodes and lasers” (Holub and Bhattacharya. J. Phys D:Appl Phys. 40(2007) R179-R203), in the state of the art, it is disclosed the spin polarized light sources and that the combinations of spin polarized carriers that will emit provide circularly polarized light.
In the article titled “Electrical Spin Injection and threshold Reduction in a Semiconductor Laser” (Holub M. et.al. Phys. Rev. Let. 98, 146603 (2007)), in the state of the art, spin polarized vertical cavity surface emitting laser with electron spin injection from Schottky tunnel barrier are shown.
In the article titled “Current Driven Domain Wall Velocities Exceeding the Spin Angular Momentum Transfer Rate in Permalloy Nanowires” (Hayashi M, et.al. Phys. Rev. Let. 98, 037204 (2007)), in the state of the art, it is disclosed that different driving mechanisms for current densities which exceeds the threshold value for transferring spin angular momentums of spin polarized electrons to the domain wall.